Sound attenuating panel with vibrating damping plate



C. W. LEMMERMAN SOUND ATTENUATING PANEL WITH VIBRATING DAMPING PLATE Original Filed July 2, 1958 2 Sheets-Sheet l FIG. 2 70 6/ 6585/ 77 a4 a5 4 9/ L3 I I .V A 92 I i I, y 63 65 a T. 65

l b/ 2 ll. 90 2 a o 90 2 I 1 64 a ,5- 66 64 7 Q g 1 f I j I l I w 4; 2 22 60 5m 85 3 7/ 86 5 60 9o @2 4J7 INVENTOR.

CARL W LE'MMERMAN WWW/WM? ATTORNEYfi 1956 c. w. LEMMERMAN SOUND ATTENUATING PANEL WITH VIBRATING DAMPING PLATE Original Filed July 2, 1958 2 Sheets-Sheet 2 United States Patent 3,235,029 SOUND ATTENUATING PANEL WITH VIBRATING DAMPING PLATE Carl W. Lemmerman, West Hartford, Conn. C. W. Lemmerman, Inc, 621 Farmington Ava, Hartford,

, Conn.)

Original application July 2, 1958, Ser. No. 746,250, now Patent No. 3,120,295, dated Feb. 4, 1964. Divided and this application May 1, 1963, Ser. No. 277,307

6 Claims. (Cl. 181-33) This invention generally relates to sound isolating enclosures and more particularly, to an improved sound panel utilized in the construction of such enclosures.

This application is a division of my parent copending application Serial No. 746,250, filed July 2, 1958, now Patent No. 3,120,295, granted February 4, 1964.

One of the objects of the present invention is to provide a sound panel having an improved construction which willeffectively attenuate sound. Included in this object is the provision of such a panel which is particularly suitable for use in the construction of sound barriers for sound frequencies such as are attendant in jet engine operation.

A further object of the present invention is to provide such an improved sound attenuating panel which is economical to manufacture, while being light in weight and durable in use, and which may be easily assembled or disassembled with respect to other panels of the same type.

Other objects will be in part obvious and in part pointed out more in detail hereinafter.

The invention accordingly consists in the features of construction, combination of elements and arrangement of parts which will be exemplified in the construction hereafter set forth and the scope of the application which will be indicated in the appended claims.

In the drawings:

FIG. 1 is a fragmental elevational view of a sound isolating enclosure wall incorporating panels constructed in accordance with the present invention;

FIG. 2 is an enlarged cross-sectional view taken generally along lines 22 of FIG. 1; and

FIG. 3 is an enlarged cross-sectional view taken generally along lines 33 of FIG. 1.

The sound panel of the invention is particularly suitable for use in the construction of sound isolating enclosures utilized in connection with aircraft engine testing where the sound or noise produced by the latter is great. Referring to the drawings in detail, FIG. 1 shows for illustrative purposes, a side wall generally designated 20, which forms a component of a sound isolating enclosure, the wall '20 being constructed from prefabricated sound attenuating panels 22, 24, and 26 embodying the "present invention. The panels as shown are supported on a concrete floor and a suitable top wall, shown dotted at 17, may comprise either like panels or in the alternative the upper margin 16 of the side Wall panels may abut a concrete or other ceiling surface forming part of the room in which the enclosure is assembled.

FIGS. 2 and 3 show similar wall constructions in that both walls include a sound blocking panel positioned outwardly of a sound absorbing panel in respect to the en closure formed by the walls, and later described in detail. FIG. 3 illustrates the internal construction of both a wall panel and a door panel as well as the marginal configuration of the door and its mating relation to vertical margins or jambs of the doorway to provide a sound insulating seal therebetween when the door is in a closed position. The sound blocking panel 60 of FIG. 2 includes the structure between an outer steel plate 62 and an inner steel plate 63, while the sound absorbing panel 61 includes the structure thereabove as viewed. A

floating septum 64 provides a partition substantially midway between the outer and inner plates of panel 60 to divide the space therebetween into to compartments 65 and 66 which are filled with a suitable sound absorbing material 67.

FIG. 2 shows the left edge of a sound blocking panel 66 interlocked with the right edge of an aligned sound blocking panel 69', panels 60 and 69 being of uniform construction. The opposite edges of panels 60 and 60, not shown, are identical to corresponding edges shown with the interlocking therebetween being identical to that herein described. The left edge 78 of compartment 65, formed by marginally channeling plate 63, is positioned in staggered relation to the left edge 71 of compartment 66 formed by the margin of plate 62 with the edge 76 and 71 in the same staggered relation as are the right hand edges 72 and 73 respectively of compartment 65' and 66 of the dual compartment sound blocking panel 60' at the left side of FIG. 2. Since edges 72 and 73 of panel 60' correspond to the right edges of panel 60, compartments 65 and 66 are of like horizontal dimension with the left edge 70 of compartment 65 offset to the left of edge 71 of compartment 66. Right edge 72 of compartment 65 is offset to the left of right edge 73 of that compartment, hence compartments 66 are horizontally offset from compartment 65 throughout the wall formed by the panels and the right edge of the adjacent sound blocking panels such as 60' mates with the left edge of a similar adjacent panel such as 60 and in that manner the panels are bolted together to provide a unitary wall construction.

Floating septum 64 is resiliently supported in panel 60 by structure at the panel margins and adjacent the brackets which bolt the panels together. As shown in FIG. 2, angle bracket 75 is fixed to the left edge of outer plate 62 of panel 68 and angle bracket 76 is secured to the right edge of corresponding outer plate 62 adjacent edge 73 of panel 60'. Rubber strips 77 form resilient spacers between ends walls 70 and 72 and end walls 70 and 73 while thinner rubber spacers 78 are maintained clamped between the anchor brackets 75 and 76 by bolts 80 to thus maintain the ends of the panels in clamped engagement with their resilient spacers with the spacers under compression. A stud 81 extends outwardly from a retainer 84 in compartment 65 which retains the stud head 83 with the shank of the stud extending through compartment 66 to be maintained clamped by nut 82 to the base of the bracket 76 and the margins of retainer 84 clamped against flange 85 of the channel forming end wall 70, flange 85 extending from end wall 70 a distance equal to flange 86 secured to end wall 71 in parallel spaced relation to flange 85 to form a channel therebetween for a resilient mount or septum isolator 88 which is centrally channeled to receive and resiliently mount a margin of the rigid steel floating septum 64. The right edge of sound blocking panel 60' is likewise provided with a septum isolator 88 mounted between flange 85' and 86 for a like purpose, isolator 88 preferably being of neoprene or similar rubber.

Floating septum 64 has secured to each side thereof a plurality of channel bar stifieners 90, V-shaped in cross section, and positioned in parallel spaced relation, with each alternate stiffener on the opposite side of the plate. The spacing between the stiffeners is selected as a definite function of the sound frequencies to be blocked. While sound blocking panels such as 60 may be maintained clamped in unitary assembly as above to form a wall such as shown in FIG. 1, it may be desirable under certain circumstances additionally to provide a sound absorbing panel 61 adjacent the inner wall surface of the sound blocking panels. Such a sound absorbing panel consists of perforate steel plates 91 and 92 maintained in parallel relation by spacers 93, FIG. 3, with plate 92 contiguous to inner plate 63 of the first mentioned panels and the space between plates 91 and 92 filled with a suitable sound absorbing material. A wire mesh 94 may be positioned adjacent plates 91, if required, to constrain the sound absorbing material from working out of the plate perforations.

It is apparent from the above description that the sound abating or isolating enclosure in which the invenive principles are incorporated consists of relatively light weight panels and a door of similar construction which are prefabricated prior to final assembly and which may be easily assembled at a test facility at any convenient location within a building or in fact outside the building, if desired. Measurements of the sound level outside enclosures constructed in accordance with the invention conclusively prove that such panels constructed of an overall thickness of 6 inches, which includes both the sound blocking and sound absorbing panel, are equal as sound barriers to a concrete panel of 12 inches total thickness. Sound isolating compartments of the concrete panel type are normally of permanent construction and must be demolished rather than disassembled when no longer useful at a particular location. While a sound isolating enclosure constructed in accordance with the invention cannot be termed portable in the normal sense of the word, such an enclosure may be disassembled and re assembled at a new location within a matter of hours, hence substantial cost savings are effected with comparable savings in down time, since several days rather than hours are required to construct a concrete enclosure.

While the invention is not to be limited by any particular theory of operation, it is believed that the effectiveness of the sound blocking panel over previous structures employing compartments filled with sound insulating material is as follows. The sound from a source such as a jet engine includes many frequencies, some of which are absorbed by the inner sound absorbing panel when employed inwardly of the sound blocking panel, it being understood that the use of an inner sound absorbing panel is optional, its use depending on the magnitude of sound to be abated. Under some conditions the wall may comprise only a sound blocking panel. The mixed frequency sound waves conveyed through air to arrive at the inner wall 63 of the sound blocking panel, whether after passing through the sound absorbing panel or not, causes panel 63 to vibrate at one of the relatively audible sound frequencies and possibly at several harmonics thereof beyond the audible range. The sound which causes the fundamental vibration of plate 63 is to a large extent absorbed by the insulating material 100 disposed between plate 63 and the septum plate 64. Sound of substantially higher frequencies from the source pass directly through plate 63 without affecting its fundamental frequency of vibration, it being well known that steel is an excellent medium for sound transmission, and that there exists no interference between sound waves of various frequencies, regardless of the medium through which sound travels in longitudinal or compression waves. While plate 63 is thus vibrating at a relatively low frequency and dissipating sound energy into the adjacent insulating material, the higher frequency sound arrives at septum plate 64 without substantial attenuation.

Septum plate 64, being floatably mounted marginally thereof and provided with transverse stiifeners 99 which function somewhat as frets on a musical instrument, is capable of vibrating as a unit at a relatively low sound frequency, but portions thereof intermediate the stilfeners vibrate at much higher frequencies than does plate 64 as a unit. The resilient isolators promote the unitary low and the sectionalized high vibrations and the high frequencies which pass through plate 63 vibrate the areas between the septum stiffeners. The natural period of vibration of the isolated areas is an upper harmonic of the high frequencies which cause them to vibrate, hence they serve as frequency convertors to remove some of the sound energy from the audible range. The insulating material on each side of the septum plate is loosely packed, hence neither the vibration of the plate as a whole or the higher vibration of the isolated areas thereof is substantially damped by that material. The stitfeners or frets 959 are mounted in parallel spaced relation at distances selected in view of the high frequency sound to be abated. The septum portions intermediate the frets thus serving to convert substantial sound energy into frequencies which are above those audible to the human ear, effectively eliminate a large portion of the sound energy as an acoustical nuisance. Since the septum plate vibrates as a unit at a relatively low frequency, the sound energy of that frequency is dissipated by energy conversion into the insulating material on each side of the septum plate. The outermost insulating material receives most of that energy, along with some of the energy which was not dissipated by the innermost layer of insulating material as a result of the transfer thereto by plate 63.

The outer wall 62 is" also vibrated by those sound waves which travel through the panel structure, but the vibration of that wall is substantially less than either wall 63 or septum 64, due to attenuation through the panel. The panel structure thus promotes dissipation of audible sound by both resonator absorption with the walls serving as a sound filter; by viscous forces which degrade the sound energy into heat; by thermal conduction and radiation; and by frequency conversion. The septum divides the space between the walls 62 and 63 into a pair of parallel sound traps which promote such dissipation in a known manner. Thus the panel simultaneously employs several effective methods of attenuation and a blending of the low level escaping sound into complex frequency patterns which are acoustically unobjectionable to persons in the immediate area surrounding the enclosure.

The construction of the door shown in FIG. 3 is quite similar to the panel construction of FIG. 2 except that single panels are employed which terminate at each side of the door and there is no need for interconnecting panels in the staggered relation above described. Numbers and fill in FIG. 3 identify compartments which are equivalent to compartments 65 and 66 of the FIG. 2 structure, and the floating septum 64 is identical to the septum given the same numeral in FIG. 2 which is also true to the stiifeners 9t), isolators 88 and the inner and outer plates 63 and 62.

FIG. 3 shows the wall panels terminating in end wall portions '70 and 71 which support isolator mounting brackets 86 for isolators 88 corresponding to like structure in FIG. 2. The door panel has opposite end wall portions 72 and 73 with brackets 86 and isolators 88 mounting floating septum 64 in the same manner as in the side wall panels.

From the above it will be seen that the present invention provides an acoustical panel which provides improved sound-attenuating results with a lightweight and economical structure that may be readily adapted to various acoustical constructions.

As will be apparent to persons skilled in the art, various modifications and adaptations of the structure above described will become readily apparent without departure from the spirit and scope of the invention, the scope of which is defined in the appended claims.

I claim:

1. A sound attenuating panel comprising a pair of parallel plates disposed in spaced apart relation, a partition disposed between said parallel plates, spacer means interconnecting said plates marginally thereof, means supported by said spacer means and engaging margins of said partition resiliently mounting said partition and means secured to said partition and spaced from said pair of parallel plates for modifying the natural period of vibration of said partition.

2. A sound attenuating panel comprising a pair of plates, means connecting marginal portions of said plates to maintain them in parallel spaced apart relation, and a third plate intermediate said pair of plates, resilient means marginally connecting said third plate to said first connecting means to permit said third plate to vibrate as a unit, and a plurality of elongate rigid elements fixed to said third plate and extending transversely thereof in parallel spaced relation for modifying the natural period of vibration of said third plate.

3. The device of claim 2 wherein the space between said pair of plates and said third plate is substantially filled with sound absorbing material.

4. The device of claim 2 wherein said plates are metal and said elongate elements are metallic angle bars welded to said third plate.

5. The device of claim 2 wherein said elongate elements are spaced at distances selected to permit the plate areas defined therebetween to vibrate at frequencies which are multiples of the fundamental frequency of the third plate as a unit.

6. A sound attenuating panel comprising a pair of metal plates, spacers interconnecting margins of said plates to maintain the plates in parallel spaced apart relation, a partition disposed between said parallel plates, mounting means including resilient connectors engaged with said partition and secured to said spacers, and metal angle bars secured to said partition in spaced parallel relation, said angle bars being equally spaced apart.

References Cited by the Examiner UNITED STATES PATENTS 1,738,670 12/1929 Rohrbach 181-33 1,841,810 1/1932 Henderson 181-33 2,079,878 5/1937 Sabine 181-33 2,081,953 6/1937 Perry 181-33 2,177,393 10/1939 Parkinson 181-33 2,196,615 4/1940 Surprenant 181-33 2,255,511 9/1941 Muller 181-33 2,270,825 l/1942 Parkinson et al 181-33 2,674,336 4/1954 Lemmerman 181-33 2,915,135 12/1959 Lemmerman 181-33 2,918,984 12/1959 Lemmerman 181-33 LEO SMILOW, Primary Examiner. 

